Lauryn

Anjali

Tarek

Lilian

Overview

So what is an urban heat island ? In a general sense, it's a phenomenon in which developed areas
experience higher temperatures than less developed areas nearby.

For example, Austin probably experiences higher average temperatures than Lago Vista, a nearby town that's much smaller and less
urbanized.

So what causes an urban heat island? As urban features like buildings, highways, and
paving reduce or replace natural features, like bodies of water and vegetation, an area's temperatures rise compared to undeveloped
areas.

Causes

Heat islands are caused by many variables. A few significant ones are

impervious cover (e.g., pavement, asphalt)

development

arrangement of buildings

sky view factor

population

weather

For example, with an increase in impervious cover , there's an associated decrease in vegetation.
But impervious cover doesn't absorb water like vegetation does, leading to an increase in run-off water.
Plus, while vegetation can cool air by evapotranspiration, impervious cover heats air!

Certain building materials that have a low albedo (or solar reflectivity) also contribute to heat island effects. Rather than
reflecting solar radiation, a lot of building materials absorb it and then emit heat to their surroundings.

But wait - how do we know heat islands exist? Let's take a look at the data!

Data

Heat islands can be studied using satellite imagery, which allows researchers to visualize and analyze the energy reflected
and emitted from Earth's surface. Instruments on satellites can measure the thermal energy emitted from surfaces as wavelengths,
creating thermal images, on which colors are associated with temperatures.
By comparing thermal images of developed and undeveloped areas, the urban heat island effect can be quantified - simply take the
difference between the temperatures of different areas and map the results.

One source of satellite images is NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS).
On board the Terra and Aqua satellites, MODIS is able to capture images of and data from the Earth’s entire surface every
1 to 2 days. In addition, MODIS can help with obtaining
historical data, helping us to understand how urban heat islands have evolved.

After collecting relevant satellite images, information can be plotted on a coordinate system, like ArcGIS, to
create a visual representation of where the peak temperature differential occurs.
A heat map of the city can be created and a fundamental heat island can be visualized.

Now that we know a little about heat islands, why should we care about them?

Water

Health

Urban heat islands cause both an increase in temperature as well as in air and water pollution. This results in major health issues
in addition to general discomfort for urban residents.

Heat islands can contribute to respiratory issues, heat stroke, water-borne
illnesses, and even mortality. The elderly and the ill are especially vulnerable sectors of the population.
Low-income urban residents are also in a vulnerable position if they lack access to air conditioning, healthy buildings, and
healthcare.